Google Analytics Vs. Webtrends Log Info - Discrepancy

It's been a longggg time since I've posted guys, but I still actively check up on you guys. Now I need help!

We use both Web Trends (logs only, no JS or cookies) and Google Analytics (JS). And we're seeing a different of nearly 50% in the count of visits in a given month.

Here are some of my thoughts - I'd love to hear yours because I am going crazy trying to find the answer:

1. We didn't have the GA tag placed on all pages - bad boys over there in IT, but this only accounted for maybe 3-5% of the "missing" visits in GA.2. GA excludes all crawlers, bots, etc. WT only excludes those on the "list". There is the list of the top 100 visitors and many of these are crawlers, bots, etc. But that still doesn't explain the 50% difference, unless there are a gazillion crawlers hitting our site for 1 or 2 visits that are outside of the top 100. Possible, but is is adding up to more than a 1 million visit difference? I dunno....3. The GA script is the bottom of the page - possible issues with single page visitors (nearly 1.9 million last month) leaving before the tag is activated? 4. Javascript disabled for users - seems this number could be anywhere from 3-6% from what I've read, but that only accounts for 17% of the "missing" visits.

Just to note that you'll also often get wildly different results if you were comparing the numbers from two stats packages that appear to use the same methods. As a for instance, two different software solutions that offer log analysis will quite often show large discrepancies. For one or more of a 100 or so different reasons. Including stuff as simple as one may only show a "hit" for a 200 OK response while another may show a "hit" for 200 OK's and 304 Not Modified's.

As Jill already said you've hit on all of the major ones I'd be looking at when you're talking about a difference between a log analyzer and an external .js analyzer. Sad to say perhaps, but no two are ever going to give you the same numbers. And often the counts will be wildly different.

That's why I tend to stick with comparing numbers within the same tool. Yes I have a log analyzer built into my sites. And yes I have GoAn on most of them. And yes I do look at both. I just never compare one to the other, expect in a rather loose manner when I see the traffic numbers go up significantly in one and want to confirm a similar rise in the other.